scholarly journals The birth environment of planetary systems

2020 ◽  
Vol 7 (11) ◽  
pp. 201271
Author(s):  
Richard J. Parker
Keyword(s):  
Planet Formation ◽  
Young Star ◽  
Giant Molecular Clouds ◽  
Secondary Effects ◽  
Star Forming ◽  
Radiation Fields ◽  
Star Forming Regions ◽  
Birth Environment ◽  
Typical Range ◽  
Protoplanetary Discs

Star and planet formation are inextricably linked. In the earliest phases of the collapse of a protostar, a disc forms around the young star and such discs are observed for the first several million years of a star’s life. It is within these circumstellar, or protoplanetary, discs that the first stages of planet formation occur. Recent observations from the Atacama large millimetre array (ALMA) suggest that planet formation may already be underway after only 1 Myr of a star’s life. However, stars do not form in isolation; they form from the collapse and fragmentation of giant molecular clouds several parsecs in size. This results in young stars forming in groups—often referred to as ‘clusters’. In these star-forming regions, the stellar density is much higher than the location of the Sun and other stars in the Galactic disc that host exoplanets. As such, the environment where stars form has the potential to influence the planet formation process. In star-forming regions, protoplanetary discs can be truncated or destroyed by interactions with passing stars, as well as photoevaporation from the radiation fields of very massive stars. Once formed, the planets themselves can have their orbits altered by dynamical encounters—either directly from passing stars or through secondary effects such as the Kozai–Lidov mechanism. In this contribution, I review the different processes that can affect planet formation and stability in star-forming regions. I discuss each process in light of the typical range of stellar densities observed for star-forming regions. I finish by discussing these effects in the context of theories for the birth environment of the Solar System.

scholarly journals External photoevaporation of circumstellar discs constrains the time-scale for planet formation

2019 ◽  
Vol 490 (4) ◽  
pp. 5678-5690 ◽  
Author(s):  
Francisca Concha-Ramírez ◽  
Martijn J C Wilhelm ◽  
Simon Portegies Zwart ◽  
Thomas J Haworth
Keyword(s):  
Time Scale ◽  
Planet Formation ◽  
Young Star ◽  
Radiation Environment ◽  
Star Forming ◽  
Star Forming Regions ◽  
Cluster Evolution ◽  
The Masses ◽  
The Impact ◽  
Young Star Clusters

ABSTRACT Planet-forming circumstellar discs are a fundamental part of the star formation process. Since stars form in a hierarchical fashion in groups of up to hundreds or thousands, the UV radiation environment that these discs are exposed to can vary in strength by at least six orders of magnitude. This radiation can limit the masses and sizes of the discs. Diversity in star forming environments can have long lasting effects in disc evolution and in the resulting planetary populations. We perform simulations to explore the evolution of circumstellar discs in young star clusters. We include viscous evolution, as well as the impact of dynamical encounters and external photoevaporation. We find that photoevaporation is an important process in destroying circumstellar discs: in regions of stellar density ρ ∼ 100 M⊙ pc−3 around $80{{\ \rm per\ cent}}$ of discs are destroyed before $2\, \hbox{Myr}$ of cluster evolution. In regions of ρ ∼ 50 M⊙ pc−3 around $50{{\ \rm per\ cent}}$ of discs are destroyed in the same time-scale. Our findings are in agreement with observed disc fractions in young star-forming regions and support previous estimations that planet formation must start in time-scales <0.1–1 Myr.

scholarly journals Double trouble: Gaia reveals (proto)planetary systems that may experience more than one dense star-forming environment

2020 ◽  
Vol 501 (1) ◽  
pp. L12-L17
Author(s):  
Christina Schoettler ◽  
Richard J Parker
Keyword(s):  
Planetary Systems ◽  
Young Star ◽  
Young Stars ◽  
Orion Nebula ◽  
External Effects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Ejection Process ◽  
Runaway Stars

ABSTRACT Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such as dynamical interactions with other stars and photoevaporation from massive stars. These interactions can also cause young stars to be ejected from their birth regions and become runaways. We present examples of such runaway stars in the vicinity of the Orion Nebula Cluster (ONC) found in Gaia DR2 data that have retained their discs during the ejection process. Once set on their path, these runaways usually do not encounter any other dense regions that could endanger the survival of their discs or young planetary systems. However, we show that it is possible for star–disc systems, presumably ejected from one dense star-forming region, to encounter a second dense region, in our case the ONC. While the interactions of the ejected star–disc systems in the second region are unlikely to be the same as in their birth region, a second encounter will increase the risk to the disc or planetary system from malign external effects.

scholarly journals The Violent Interstellar Medium of Nearby Dwarf Galaxies

1999 ◽  
Vol 16 (1) ◽  
pp. 106-112 ◽  
Author(s):  
Fabian Walter
Keyword(s):  
Interstellar Medium ◽  
Gamma Ray ◽  
Dwarf Galaxies ◽  
Young Star ◽  
Stellar Winds ◽  
Star Forming ◽  
Star Forming Regions ◽  
Supernova Explosions ◽  
High Velocity Clouds ◽  
Ob Associations

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

scholarly journals ALMA survey of Class II protoplanetary disks in Corona Australis: a young region with low disk masses

2019 ◽  
Vol 626 ◽  
pp. A11 ◽  
Author(s):  
P. Cazzoletti ◽  
C. F. Manara ◽  
H. Baobab Liu ◽  
E. F. van Dishoeck ◽  
S. Facchini ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Mass Distribution ◽  
Planet Formation ◽  
Protoplanetary Disks ◽  
Class Ii ◽  
Star Forming ◽  
Star Forming Regions ◽  
Disk Mass ◽  
Intrinsic Angular Momentum ◽  
Dust Mass

Context. In recent years, the disk populations in a number of young star-forming regions have been surveyed with the Atacama Large Millimeter/submillimeter Array (ALMA). Understanding the disk properties and their correlation with the properties of the central star is critical to understanding planet formation. In particular, a decrease of the average measured disk dust mass with the age of the region has been observed, consistent with grain growth and disk dissipation. Aims. We aim to compare the general properties of disks and their host stars in the nearby (d = 160 pc) Corona Australis (CrA) star forming region to those of the disks and stars in other regions. Methods. We conducted high-sensitivity continuum ALMA observations of 43 Class II young stellar objects in CrA at 1.3 mm (230 GHz). The typical spatial resolution is ~0.3′′. The continuum fluxes are used to estimate the dust masses of the disks, and a survival analysis is performed to estimate the average dust mass. We also obtained new VLT/X-shooter spectra for 12 of the objects in our sample for which spectral type (SpT) information was missing. Results. Twenty-four disks were detected, and stringent limits have been put on the average dust mass of the nondetections. Taking into account the upper limits, the average disk mass in CrA is 6 ± 3 M⊕. This value is significantly lower than that of disks in other young (1–3 Myr) star forming regions (Lupus, Taurus, Chamaeleon I, and Ophiuchus) and appears to be consistent with the average disk mass of the 5–10 Myr-old Upper Sco. The position of the stars in our sample on the Herzsprung-Russel diagram however seems to confirm that CrA has an age similar to Lupus. Neither external photoevaporation nor a lower-than-usual stellar mass distribution can explain the low disk masses. On the other hand, a low-mass disk population could be explained if the disks were small, which could happen if the parent cloud had a low temperature or intrinsic angular momentum, or if the angular momentum of the cloud were removed by some physical mechanism such as magnetic braking. Even in detected disks, none show clear substructures or cavities. Conclusions. Our results suggest that in order to fully explain and understand the dust mass distribution of protoplanetary disks and their evolution, it may also be necessary to take into consideration the initial conditions of star- and disk-formation process. These conditions at the very beginning may potentially vary from region to region, and could play a crucial role in planet formation and evolution.

scholarly journals A Denis Survey of Star Forming Regions

1998 ◽  
Vol 179 ◽  
pp. 172-174 ◽  
Author(s):  
E. Copet
Keyword(s):  
Molecular Clouds ◽  
Stellar Population ◽  
Giant Molecular Clouds ◽  
The South ◽  
Large Format ◽  
Star Forming ◽  
Star Forming Regions ◽  
Array Detectors

A complete census of embedded stellar population can be made by exploring in the infrared large areas of the sky in which giant molecular clouds extend. Very recently, thanks to the of large format IR array detectors, studies of young stellar population in GMCs, have been undertaken by different authors (i.e., Lada et al. 1991) but all these observations were limited to relatively small regions of the whole GMCs, the DENIS project (Epchtein, this volume, p. 106) surveys the south hemisphere at I, J and Ks bands, including most of these clouds.

scholarly journals Chemistry in the Envelopes around Massive Young Stars

2002 ◽  
Vol 12 ◽  
pp. 146-148
Author(s):  
Ewine F. van Dishoeck ◽  
Floris F.S. van der Tak
Keyword(s):  
Young Star ◽  
Young Stars ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Chemical Studies ◽  
H Ii Region ◽  
Infrared Wavelengths ◽  
Collapse Phase

AbstractRecent chemical studies of high-mass star-forming regions at submillimeter and infrared wavelengths reveal large variations in the abundances depending on evolutionary state. Such variations can be explained by freezing out of molecules onto grains in the cold collapse phase, followed by evaporation and high-temperature chemical reactions when the young star heats the envelope. Thus, the chemical composition can be a powerful diagnostic tool. A detailed study of a set of infrared-bright massive young stars reveals systematic increases in the gas/solid ratios and abundances of evaporated molecules with temperature. This ‘global heating’ plausibly results from the gradual dispersion of the envelopes. We argue that these objects form the earliest phase of massive star formation, before the ‘hot core’ and ultracompact H II region phase.

scholarly journals Astrometry in the Service of Planet Formation Studies: Disk Lifetimes in Nearby Star Forming Regions and a Planet Candidate around a Mature Brown Dwarf

2013 ◽  
Vol 8 (S299) ◽  
pp. 230-231
Author(s):  
Alycia J. Weinberger ◽  
Alan P. Boss ◽  
Guillem Anglada-Escudé
Keyword(s):  
Planet Formation ◽  
Circumstellar Disks ◽  
Giant Planets ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass ◽  
Stellar Associations

AbstractWe present preliminary astrometric results aimed at understanding the lifetime of circumstellar disks and potential for planet formation. We have obtained parallaxes to stars in the TW Hydrae, Upper Scorpius, and Chamaeleon I stellar associations. These enable new estimates for the ages of the stars. We are also performing the Carnegie Astrometric Planet Search of nearby low mass stars for gas giant planets on wide orbits. We have our first candidate around a mature brown dwarf.

scholarly journals Disk Masses and Dust Evolution of Protoplanetary Disks around Brown Dwarfs

2021 ◽  
Vol 921 (2) ◽  
pp. 182
Author(s):  
Anneliese M. Rilinger ◽  
Catherine C. Espaillat
Keyword(s):  
Planet Formation ◽  
Spectral Energy ◽  
Star Forming ◽  
Star Forming Regions ◽  
Disk Mass ◽  
T Tauri ◽  
Multiple Regions ◽  
Disk Evolution ◽  
Dust Grain ◽  
Dust Evolution

Abstract We present the largest sample of brown dwarf (BD) protoplanetary disk spectral energy distributions modeled to date. We compile 49 objects with ALMA observations from four star-forming regions: ρ Ophiuchus, Taurus, Lupus, and Upper Scorpius. Studying multiple regions with various ages enables us to probe disk evolution over time. Specifically, from our models, we obtain values for dust grain sizes, dust settling, and disk mass; we compare how each of these parameters vary between the regions. We find that disk mass decreases with age. We also find evidence of disk evolution (i.e., grain growth and significant dust settling) in all four regions, indicating that planet formation and disk evolution may begin to occur at earlier stages. We generally find that these disks contain too little mass to form planetary companions, though we cannot rule out that planet formation may have already occurred. Finally, we examine the disk mass–host mass relationship and find that BD disks are largely consistent with previously determined relationships for disks around T Tauri stars.

scholarly journals Runaway and walkaway stars from the ONC with Gaia DR2

2020 ◽  
Vol 495 (3) ◽  
pp. 3104-3123 ◽  
Author(s):  
Christina Schoettler ◽  
Jos de Bruijne ◽  
Eero Vaher ◽  
Richard J Parker
Keyword(s):  
Initial Conditions ◽  
Young Star ◽  
Three Dimensions ◽  
Orion Nebula ◽  
Star Forming ◽  
Star Forming Regions ◽  
Trace Back ◽  
Runaway Stars ◽  
Gaia Dr2 ◽  
Age Estimates

ABSTRACT Theory predicts that we should find fast, ejected (runaway) stars of all masses around dense, young star-forming regions. N-body simulations show that the number and distribution of these ejected stars could be used to constrain the initial spatial and kinematic substructure of the regions. We search for runaway and slower walkaway stars within 100 pc of the Orion Nebula Cluster (ONC) using Gaia DR2 astrometry and photometry. We compare our findings to predictions for the number and velocity distributions of runaway stars from simulations that we run for 4 Myr with initial conditions tailored to the ONC. In Gaia DR2, we find 31 runaway and 54 walkaway candidates based on proper motion, but not all of these are viable candidates in three dimensions. About 40 per cent are missing radial velocities, but we can trace back nine 3D runaways and 24 3D walkaways to the ONC, all of which are low/intermediate mass (<8 M⊙). Our simulations show that the number of runaways within 100 pc decreases the older a region is (as they quickly travel beyond this boundary), whereas the number of walkaways increases up to 3 Myr. We find fewer walkaways in Gaia DR2 than the maximum suggested from our simulations, which may be due to observational incompleteness. However, the number of Gaia DR2 runaways agrees with the number from our simulations during an age of ∼1.3–2.4 Myr, allowing us to confirm existing age estimates for the ONC (and potentially other star-forming regions) using runaway stars.

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